The point is to get information even when the source is not willing to go on public record as having said it.
examples:
* The reporter may be wanting to gain information, either “deep background” to understand things they won’t report in direct detail about, or confirmation of information from other sources, or to debunk a rumor so they don’t mis-report something, or whatever.
* A source has inside information that would have negative effects on the source (e.g. scandal, get them fired/divorced, or worse) if they publicly made a statement about it, but they have moral reasons for wanting the public to know the information.
* A source has inside information that they aren’t allowed to publicly discuss, but giving some confidential off-the-record information to a reporter may tend to have a positive effect on what the reporter publishes (e.g. because it will inform their perspective).
* A source might have reasons not to be cited, but has information that will lead the reporter to other research and/or sources who may be willing to be cited.
@kritiper heresy is a religious issue; hearsay is when a piece of information’s basis is one merely heard someone say something.